We are resubmitting a paper. One co-author was part of the project from the beginning, assisted in all group discussions, gave intellectual feedback, but did not do any experiments/analyses. He also wrote a small part of the discussion. What should I write regarding his/her contributions in the respective section?
This does not sound like a special case at all, but rather like a typical contribution of a supervisor. When describing such a co-author’s contributions, I would let myself be inspired by other similar descriptions for supervisors. The definite answer may depend on the particular style of this section and details of the contribution, but one suggestion would be:
X designed the study, supervised the research, and wrote the manuscript.